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Predators Foraging on Endosymbiotic Containing Paramecium Catalyze Chloroviruses Population in the Ecosystem
For millions of years, viruses have played an important role due to their influence on marine ecosystems. With over 70% of Earth’s surface being covered by water, there is an enormous number of viruses that are yet to be discovered or thoroughly researched. Today’s technology brings forth greater and more enhanced methods to study and prove the importance of the role of viruses as part of the marine community structure, both on a global and miniscule scale. Viruses influence the biogeochemical cycle, gene transfer, disruption of algal blooms, and evolution of aquatic organisms. Even difficult and harsh environmental conditions do not hinder the aquatic viruses’ role in the cycling of carbon and nutrients within the water. One motivation for focusing on specific viruses is that they can play a significant role in the environment, but especially if the virus might also infect humans. One group of viruses that meet both of these criteria is the chloroviruses (family Phycodnaviridae) that are unique and have been studied for about the last 40 years. They serve as an interesting model for large, icosahedral, double stranded DNA viruses (genomes between 270 to 370 kb), which infect eukaryotic algae and presumably influence the aquatic environment. Furthermore, certain chlorovirus members may possibly influence cognitive behaviors in humans; however, this aspect is still under study as there is much to learn about this possible aspect of the viruses. Chloroviruses are common in freshwater environments. They replicate in eukaryotic, single-celled, chlorella-like green algae, which exist naturally as endosymbionts of protists. The chloroviruses are not only extremely abundant but are also diverse. Increases in chlorovirus populations occur as more viruses come into contact with their hosts, and frequently, there are spikes in viral abundance. Ongoing experiments, including those described in this thesis, are trying to determine how contact between chloroviruses and their hosts occur in order to generate these chlorovirus fluctuations. In our research, we established that predators can feed on Paramecium bursaria, which naturally have virus particles attached to their outer cell membrane. P. bursaria harbor several hundred algae inside their cytoplasm, which are the host algae for many of the chloroviruses. In this thesis we show that predators of P. bursaria, like copepods, can release these algae by disrupting the paramecia by one of two methods. One method is referred to as ‘messy feeding’, which occurs when the copepods chew off part of the P. bursaria causing the zoochlorellae to be released into the water column where they can easily be infected by viruses. The second method is referred to as ‘whole feeding’ in which the copepods consume the entire paramecium. This pathway is primarily responsible for increasing virus populations by increasing the contact between the virus and its host (zoochlorellae) inside the copepod’s gut. In addition, fecal pellets released by the copepods also have the ability to generate more virus and result in high viral populations. The second chapter of this thesis explains how copepods function as an “ecological catalyst.” Additions groups of predators of P. bursaria were discovered which have both direct and indirect association with chlorovirus expansion and their host. In the third chapter, we establish that the ciliate Didinium nasutum is a predator that also forages on paramecia by messy feeding and that this also leads to an increase in chlorovirus populations. Furthermore, in this chapter, we examine the effect of the size of the didinium on viral population growth. Small size didinia have a highly positive effect on viral growth in the water system. The third group of predators of P. bursaria that we studied (chapter 4) are referred to as giant ciliates, including Bursaria truncatella. They prey on paramecia primarily by whole feeding, but occasionally exhibit messy feeding. Both of these methods help to slightly increase virus populations and sustain them in nature. Finally, in the last chapter, we compared several other possible predators to see if they had an effect on chlorovirus abundance. Only nematodes were shown to increase chlorovirus populations, but this is still under study.
Al-Ameeli, Zeina Tariq, "Predators Foraging on Endosymbiotic Containing Paramecium Catalyze Chloroviruses Population in the Ecosystem" (2020). ETD collection for University of Nebraska - Lincoln. AAI28086075.